---
id: CVE-2026-74989
title: Internally found bugs fixed in Firefox 154
summary: >-
  Internally found bugs present in Firefox 153. Some of these bugs showed
  evidence of memory corruption or another security-relevant defect and we
  presume that with enough effort some of these could have been exploited. This
  vulnerability …
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: adp
vendor: Mozilla
product: Firefox
affected:
  - Firefox
  - Thunderbird
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-08-20T15:50:43.213805Z'
published: '2026-08-18'
updated: '2026-10-28'
sourceUpdated: '2026-10-28T16:36:02.550Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-74989'
references:
  - url: >-
      https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022257%2C2027351%2C2027380%2C2029289
    label: Low Severity internally found bugs fixed in Firefox 154
  - url: >-
      https://bugzilla.mozilla.org/buglist.cgi?bug_id=2027388%2C2029750%2C2029794%2C2043298%2C2045126%2C2049810%2C2051741
    label: Moderate Severity internally found bugs fixed in Firefox 154
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-74/'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-78/'
tags:
  - cve.org
epss: 0.0057
epssPercentile: 0.4728
ingestedAt: '2026-10-28T17:14:44.473Z'
---

## Overview

Internally found bugs present in Firefox 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154 and Thunderbird 154.

## Affected

- `Firefox`
- `Thunderbird`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.